This invention relates to apparatus for collecting solar energy. The invention relates more particularly to an improved arrangement for efficiently collecting diffuse solar energy from the hemisphere in front of the apparatus.
Various techniques and arrangements have beem employed through the years in an attempt to utilize the radiant energy of the sun. Apparatus provided for this purpose take into account two characteristics of solar energy and its source which to a large degree control the structure and arrangement of the solar energy gathering apparatus. The first characteristic relates to the fact that solar energy is radiant energy which occurs in the form of a wavefront or flux and is extended over an area so as not to form a relatively concentrated source of energy. While certain relatively low temperature operating devices such as planar arrays of solar panels are adapted to obtain energy directly from the sun in this form, other devices require a relatively greater concentration of energy and therefore require a means for concentrating solar flux on a body or area. This means generally comprises a reflector which causes directly incident rays of solar energy to be reflected toward a focal point where a utility body is positioned for impingement by the concentrated rays of energy.
The second characteristic of solar radiant energy is its continuous, periodically varying change of oncoming direction as determined by the earth's relationship to the sun in the solar system. The continuous relative motion between the earth and sun causes the position of the sun with respect to a location on earth to vary both daily and seasonally. The hour angle and thus the altitude of the sun varies continually during a solar day with respect to the horizon. Since the sun's position or altitude during the solar day will vary with respect to a fixed point on earth, the reflector is required to track the position of the sun in the sky in order to maintain the utility body and its focal point and to provide for efficient gathering and concentration of solar energy throughout the day. Apparatus adapted to track the sun requires a relatively complex and costly arrangement for providing motion of the reflector and/or corresponding motion of the utility body. In order to simplify this arrangement, various combinations of plano reflectors such as heliostats have been provided for reducing the required motion and the complexity of the arrangement. In other arrangements the reflector is stationary and the utility body tracks the focus of the reflector with the motion of the sun in the sky. In other such apparatus, the complexity is greatly reduced at the sacrifice of efficiency by providing a stationary disc shaped reflector, modified somewhat from a parabola, and a stationary utility body which is spaced from the focal point of the reflector so as to be impinged by a relatively-high, average solar energy during the period of time when the position of the sun falls within a particular range of altitudes.
In general, the prior systems are arranged for collecting direct, incident radiant solar energy. As such, they are subject not only to the variations in the position of the sun during the solar day but also to seasonal variations in declination of the sun and to daily variations in weather. Between the spring and fall equinoxes, the declination of the sun is north and increases to about 27.5.degree. in mid June. Locations on earth in the northern hemisphere are then exposed to longer periods of solar energy at relatively higher declinations than locations in the southern hemisphere. Conversely, between the fall and spring equinoxes, the declination of the sun is south and locations in the southern hemisphere experience greater exposure to sun during a solar day. Furthermore, atmospheric cloud cover and the like shade the earth from the solar energy and can seriously interfere with efficient gathering of solar energy.
Heretofore, attempts in usefully collecting solar energy have been principally directed toward efficiently gathering direct solar energy. Diffuse solar energy generally exhibits a relatively lower energy content per unit area than does direct solar energy and because of its diffuse characteristic, it has been relatively difficult to efficiently gather or collect. However, this form of solar energy is generally more uniformally available throughout the day and is substantially more independent of seasonal and weather variations than is direct solar energy. It would be beneficial to provide a means capable not only of collecting direct solar energy but also adapted for efficiently collecting diffuse solar energy.
Accordingly, it is an object of this invention to provide an improved apparatus for collecting solar energy.
Another object of the invention is to provide an improved apparatus for collecting diffuse solar energy.
Another object of the invention is to provide a relatively efficient apparatus for the collection of diffuse solar energy.
A further object of the invention is to provide a solar energy collection adapted for efficiently collecting diffuse solar energy and for collecting direct solar energy.